Vehicle collision avoidance systems are required to accurately detect objects, such as a vehicle other than an own vehicle that is a vehicle carrying the system and a pedestrian. For example, a vehicle collision avoidance system as disclosed in Patent Literature 1 is configured to detect objects using a radar and a camera. More specifically, the disclosed vehicle collision avoidance system uses a millimeter-wave radar and a monocular camera separately, and if a positional relationship between an object detected by the millimeter-wave radar and an object detected by the monocular camera meets a predetermined criteria (particularly, if these objects are in proximity to each other), determines that these objects are the same object.